Since 1987, the UW (University of Washington)and GHC/CHS(Group Health Cooperative/Center for Health Studies) Alzheimer's Disease Patient Registry (ADPR) and Adult Changes in Thought (ACT) Study has established itself as a model incident case-finding registry as well as developed a prospective cohort of over 3,300 persons, initially without dementia. The ACT inception cohort, established 1994-96, was designed to detect new cases of dementia (especially AD), and to collect prospective data to identify potentially modifiable risk factors for AD and related conditions. To date, 309 persons have developed dementia, with an additional 291 cases projected in the near future, for a total of 600 cases. The combination of prospectively collected data over time (baseline & biennial follow-ups), plus comprehensive medical and pharmacy historic records for 10 to 20 years (median GHC membership is 19 years prior to enrollment), creates unparalleled opportunity for analyses using the ACT cohort data in the coming 5 years. The specific aims for this next cycle are: 1. To undertake innovative analyses of the pharmacoepidemiology of dementia and AD; specifically antihypertensive agents, post-menopausal hormone replacement therapy, HMC-CoA reductase inhibitors ("statins") and other antihyperlipidemic agents, non-steroidal anti-inflammatory drugs (NSAIDs), histamine H2 receptor antagonists, and antioxidant vitamins. 2. To evaluate other potential risk factors for AD and dementia, with emphasis on vascular risk factors, capitalizing on the rich ACT and GHC data sources to investigate: blood pressure, plasma lipids, exercise history, obesity, diabetes, and tobacco use. 3. To continue to serve as a vital source of long-term, comprehensive data and well-characterized research subjects for other investigators. The results of these studies will be invaluable to the development and testing of strategies to reduce the risk of AD and related conditions, and to reduce the burden of cognitive decline in the growing population of older persons.